Up and down revving issues

most modern engines are interference designed. keeps the engine profile smaller for fitment in the engine bay. I have successfully straightened valves on a 2.7 V6 honda engine that snapped the cambelt. Just revved the heck out of it once the new belt was on. All ok afterwards. Did you shut down as soon as the belt jumped the cog ?

Check belts for proper tension check output on alternator. When you turn on the a.c. it puts a drag on the engine which slows down the engine could be the alternator going bad try revving up the engine with the a.c. on to see if the light goes out. Listen for squealing belt indicating a bad belt tensioner or worn belt out of adjustment. Hope this helps also check for worn wires going to the compressor m as king sure there are no worn exposed wires grounding out on the engine or frame causing a short in the system. Hope this helps.

Dan h described what would happen if your timing belt/chain broke.. fortunately the consiquences aren't as dire if your SERPENTINE belt snaps. Most vehicles have the following systems or devices powered by the front engine accessory drive belt (FEAD belt)
AC compressor
Power steering pump
Alternator
Fan (some vehicles do and some don't)
Water pump

All but one of these things can be lived without, at least for a short time. If your belt snaps and your water pump stops your engine will overheat in no time flat., say you're cruising through a rural area and your belt snaps a mile and a half away from the next town, your car will get you there, but you had better turn it off once you get into town. After a belt snaps you've got 2 miles before you absolutely need to shut your car down to avoid damage.

If the engine is running and the battery light is coming on then there is a problem with the alternator. This is the component that charges the battery when the engine is running. If not attended to soon it will result in a flat battery.

The alternator is driven by the fan belt so I suggest checking that it is not snapped off or slipping badly.

Good luck!

Check your alternator if you can get it to start and stay running. If not then you may want to consider taking it off the car and having a parts store bench test it. It's most likely that.

Do they just dim a bit? If so, you're probably noticing the reduction in voltage from the engine belt being asked to drive the power steering pump. The engine belt also turns the alternator, which isn't getting as much power from the belt that's now doing 2 jobs. You don't notice this when you're driving because the engine RPMs are higher and the voltage from the alternator is constant. When you're stopped the engine RPMs will drop a bit and so does the voltage available for the lights. You can test this by revving the engine when you are stopped (be sure you are in neutral) and turning the wheel. You shouldn't see the light's flicker when you have the revs up. Let me know if that was the issue.

yes you do need a mechanic to check it out who installed your alternator

check the battery voltage and alternator

Remove the belt from any pulley. Go from pulley to pulley and make sure they are all free wheeling obviously you won't be able to turn the crank pulley. Spin your alternator pulley and listen to it. It should be silent and smoothe. If you hear any bearing noise from the tensioner, the alternator, the AC comppresor, I would do this soon, you've spent on belts what an alternator would cost.Also check the idler pulley if this is a serpentine type belt.

loosen the alternator and push the alternator to-wards the engine,put your new belt on ,fitting around the 3 pulleys once fitted look and see that the belt is in line.If your happy the belt is lined put a small bar between the engine and alternator and force the alternator out towards the front this should tension your belt tighten bolts on alternator.;at the longest point between two pullys in the middle of the belt move belt up and down with fingers if tension is right it should not move more than about 150ml,hope this helps you.adrian